JP2003121303A - Method for measuring wavelength dispersion and optical transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for measuring the wavelength dispersion of an optical transmission line without disconnecting a circuit, and an optical transmission system in which high quality transmission is realized by performing dispersion compensation neither too much nor too less when the optical transmission line is switched in the optical level using such a measuring method. SOLUTION: A signal for measurement is transmitted, along with a main signal, from a first node during operation of a circuit, the signal for measurement is extracted and turned back at an opposite node, a delay time required for turning back the signal for measurement is measured and the distance of an optical transmission line between the nodes is calculated at the first node, and then the wavelength dispersion of that optical transmission line is calculated based on that distance. Alternatively, a plurality of signals in a wavelength band not used as the main signal or a pulse signal of such a frequency as having substantially no effect on the main signal is delivered while being superposed on the main signal during operation of the circuit, the signal for measurement is measured at the opposite node and a delay time is measured from the difference of arriving time thereof, and then the wavelength dispersion is calculated from the wavelength dependency between the delay times. Furthermore, a plurality of opposite nodes are present and the first node switches the optical transmission line to an optimal one selected based on the calculated or collected wavelength dispersion of each optical transmission line.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of measuring a chromatic dispersion amount and an optical transmission system, and more particularly to a method of measuring a chromatic dispersion amount when transmitting a wavelength division multiplexing (WDM) signal using an optical transmission line and the method. The present invention relates to an optical transmission system using such a measuring method.

[0002]

2. Description of the Related Art Wavelength division multiplexing (WDM) optical transmission for collectively transmitting several tens to several hundreds of wavelengths in one optical fiber in order to meet the rapidly growing demand for information transmission with the rapid spread of the Internet. Systems have been developed and are being introduced rapidly. The transmission rate per wavelength is currently 2.4 Gb / s, but it is expected to exceed 10 Gb in the future.
It is predicted to replace / s, and a 40 Gb / s system is currently under development.

[0003]

2. Description of the Related Art There are several methods of constructing the WDM optical transmission system as described above. The simplest method is as shown in FIG. ) Point-to-point (P-) that multiplexes n wavelengths by TERM1 and amplifies the attenuated optical signal by the relay amplification node ILA to the receiving station (optical terminal node) TERM2 without changing the multiplexing state. P) method.

Further, FIG. 2B shows a transmitting node TERM.
1 and the optical add / drop between the receiving node TERM2
There is also known an optical transmission system in which an (OADM) node is inserted and a part of wavelengths in a wavelength division multiplexed optical signal is added and dropped by a wavelength selecting means such as an optical bandpass filter.
In this case, since the processing is performed at the light level, the functions of light / electricity and electric / light conversion are not required.

Further, FIG. 3 (3) shows an optical cross connect.
A configuration example of (OXC) (2 × 2 in this case) is shown, and in this case, the demultiplexing / combining and switching functions at the optical level realize the switching function in wavelength units. . Also in the case of this optical cross connect, the functions of optical / electrical conversion and electric / optical conversion are not required.

As described above, since the number of WDM wavelengths has been increased to several hundreds of channels, transponders (optical / electrical conversion are performed to regenerate a signal for the number of wavelengths) at the transmitting node and the receiving node, and the modulation format It is necessary to prepare a device for converting the wavelength or converting the wavelength to connect to another device, which increases the cost.

In view of this, conversion to an optical add / drop system or an optical cross-connect system, which can flexibly switch optical paths and does not require optical / electrical conversion and electric / optical conversion, is expected. Therefore, development is currently underway to realize these optical transmission systems at low cost.

[0008]

In the point-to-point system shown in FIG. 24 (1), which is the mainstream of the WDM optical transmission system at present, the transmission rate per wavelength is increased as described above. As the 1-bit time slot becomes shorter, the wavelength band of the modulation signal spectrum also widens, and waveform distortion (pulse broadening) due to wavelength dispersion causes intersymbol interference, which limits the transmission distance. Will be a factor.

Therefore, a technique of dispersion compensating the chromatic dispersion accumulated by the optical fiber transmission line in the relay amplification node has become important, and a dispersion compensating fiber (DCF) having a chromatic dispersion amount opposite to that of the optical fiber is used. Then, a technique for adjusting the total chromatic dispersion amount to zero is used.

In order to design the chromatic dispersion amount of such a dispersion compensating fiber, it is necessary to know the chromatic dispersion amount of the installed optical transmission line. The most reliable method is to measure chromatic dispersion characteristics. For example, (1)
As described in Japanese Patent Laid-Open No. 8-334436, a method of measuring the wavelength dependence of the transmission delay time of an optical pulse using a variable wavelength light source, and differentiating this with respect to the wavelength, and (2) Japanese Patent Laid-Open No. 8- OTDR (Optical Time Domai
A method has been already proposed, for example, using n Reflectometry) to measure the component reflected by backward Rayleigh scattering in the middle of the optical transmission line.

When it is not possible to actually measure the chromatic dispersion amount, the transmission distance is calculated from the measured value of the loss of the installed optical transmission line, and the catalog value of the optical fiber parameter or an equivalent characteristic is calculated. The method of estimating the chromatic dispersion amount of the installed optical transmission line from the measured value of the optical fiber is used.

As described above, it is necessary to measure the chromatic dispersion amount of the optical transmission line used in advance, or to estimate the chromatic dispersion amount from the transmission line length and the span loss amount based on the specifications of the optical fiber. A method of determining the chromatic dispersion amount of a dispersion compensation fiber is common, but FIG.
It is expected that it will be difficult to apply the above method to the optical add / drop method shown in (2) and the optical cross connect method shown in (3) for the following reasons.

That is, for example, in an optical network having an optical cross-connect function, as can be seen from (3) in the figure, when there are generally N nodes, there will be N × N logical paths. Further, even when reaching the same node, a plurality of paths (routes) can be considered, so that more combinations of paths can exist.

In order to perform transmission without causing a failure even when the path is switched among such many paths, it is safest to completely perform dispersion compensation on all paths in advance. As a result, the flexibility of the switching configuration is limited, and the characteristics of the optical fiber are significantly changed from the single mode fiber (SMF) to the non-zero dispersion shift fiber (NZDSF) due to the switching of the path. Therefore, it is difficult to set the chromatic dispersion amount to zero in all paths.

Further, it is unrealistic to perform the above-mentioned chromatic dispersion amount measurement on all of such a huge number of paths in advance, and in the case where a new path is added. In this case, the measurement must be redone for all newly created paths. In such a case, there is a problem that the already operated line must be disconnected once.

Further, a method of collectively compensating the dispersion amount of all WDM wavelengths by one dispersion compensating fiber is generally used because it is advantageous in terms of cost, but the wavelength dispersion amount of an optical fiber has wavelength dependency. Therefore, as shown in (1) and (2) of FIG. 25, the amount of dispersion increases as the transmission node TERM1 advances to the reception node TERM2, and the optimum dispersion compensation between the channels of the shortest wavelength and the longest wavelength is performed. The amount will be different.

Therefore, in order to completely compensate the chromatic dispersion amount, it is necessary to perform designing in consideration of the accumulation of such chromatic dispersion amount shifts, but it is necessary to take wavelength dependency into account when designing. It would be even more difficult to completely perform dispersion compensation on the path.

For the above reasons, it is difficult to apply the current dispersion compensation amount design method to a WDM optical transmission system incorporating the functions of the optical add / drop system and the optical cross-connect system. was there. Therefore, in order to solve the above problems, the present invention provides a method for measuring the chromatic dispersion amount of an optical transmission line without disconnecting the line, and an optical transmission line is measured using such a measuring method. An object of the present invention is to provide an optical transmission system that realizes high-quality transmission by performing dispersion compensation exactly when switching at the optical level, and thereby realizing high-quality transmission.

[0019]

In order to solve the above problems, the method of measuring the amount of chromatic dispersion according to the present invention is the first method for transmitting the measurement signal together with the main signal from the first node during the line operation. Step, a second step of extracting and returning the measurement signal at the opposite node, and a delay time required for returning the measurement signal at the first node to calculate the distance of the optical transmission path between the nodes. Then, a third step of calculating the chromatic dispersion amount of the optical transmission line based on the distance is provided.

That is, in the chromatic dispersion amount measuring method according to the present invention, a measurement signal other than the main signal is used for transmission during line operation, and the opposite node returns the measurement signal after returning it. The delay time required for this turnaround is measured, and the distance of the optical transmission line is estimated from this delay time. Since the dispersion coefficient of the optical transmission line is usually known in advance, the dispersion amount in the optical transmission line section can be calculated by applying this dispersion coefficient to the distance of the optical transmission line. .

As described above, according to the present invention, the chromatic dispersion amount of the optical transmission line between the nodes can be obtained without disconnecting the line. As the measurement signal, a supervisory control signal wavelength-division multiplexed with the main signal can be used.

The measurement signal is a wavelength tunable light source signal which is wavelength-multiplexed and multiplexed with the main signal, and is the first signal.
The chromatic dispersion amount can be calculated from the wavelength dependence of the plurality of delay times obtained by transmitting the measurement signals of a plurality of wavelengths in steps and repeating the measurement of the delay times in the third step.

That is, a variable wavelength light source is prepared in addition to the main signal, a measurement pulse is transmitted using this, and the opposite node receives this pulse and then returns it by returning it, thereby delaying the return. Measure time. Then, the chromatic dispersion amount can be obtained from the wavelength dependence of the delay time (delay time for each wavelength) obtained by repeating this measurement while changing the wavelength.

This eliminates the need for information on the amount of chromatic dispersion required for each type of optical fiber, and can flexibly support future expansion of types of optical fiber. Further, this wavelength tunable light source may be used as the above-mentioned supervisory control channel. In the above-mentioned second step, the measurement signal can be returned as it is as an optical signal or via optical / electrical conversion.

The first step sends the measurement signal to the uplink or downlink of the first node, and the second step sends the measurement signal to the same line to avoid crosstalk. It is also possible to fold it back. This allows
Rather than using another optical transmission line as a return line for returning the measurement signal, a bidirectional measurement signal can be obtained with one optical transmission line without crosstalk.

As the above-mentioned measurement signal, signals of different frequencies can be used on the same line. Further, the chromatic dispersion amount measuring method according to the present invention comprises a first step of simultaneously transmitting a plurality of measurement signals in a wavelength band not used as a main signal from the first node during line operation, and a measurement at the opposite node. The second step of extracting a signal, measuring the delay time from the arrival time difference, and calculating the chromatic dispersion amount from the wavelength dependence of the delay time can also be used.

That is, in the case of the present invention, a plurality of measurement signals are arranged in the wavelength band not used as the main signal, the measurement signals are simultaneously transmitted during the line operation, and the opposite nodes receive the measurement signals. The wavelength dependency of the delay time is obtained from the time delay difference, and the chromatic dispersion amount is further calculated from this wavelength dependency.

In this case, unlike the above-described method of the present invention, since the delay between the signals received at the opposite node side is measured, it is not necessary to return the measurement signal, so that the uplink and downlink lines between the nodes are not measured. It is also applicable to the case where is asymmetric. Further, by combining with the above wavelength tunable light source, it becomes possible to perform more accurate measurement regarding wavelength dependence.

Further, the chromatic dispersion amount measuring method according to the present invention is such that the first node superimposes on the main signal a pulse signal having a frequency that does not substantially affect the main signal and sends it out during line operation. 1 step, a second step of measuring a delay time from the arrival time difference between the pulse signals at the opposite node, and calculating a chromatic dispersion amount from the wavelength dependence of the delay time;
You may comprise.

That is, by superimposing on the main signal a signal that is sufficiently slower than the signal speed and has a small modulation factor, it is used as a measurement signal for the maximum number of WDM wavelengths, and measurement signals from a plurality of wavelengths are simultaneously obtained. At the opposite node, the wavelength dependence of the delay time can be obtained from the delay difference of the arrival time of the measurement signal at the opposite node, and the chromatic dispersion amount can be calculated.

An optical transmission system for realizing the above-mentioned chromatic dispersion amount measuring method is composed of a plurality of nodes, and a measurement signal together with a main signal is transmitted from the first node during line operation, and the opposite node transmits the measurement signal. The measurement signal is extracted and folded back, the delay time required for folding the measurement signal is measured at the first node to calculate the distance of the optical transmission line between the nodes, and the optical transmission line is calculated based on the distance. It is possible to calculate the chromatic dispersion amount.

As the above-mentioned measurement signal, as in the method of the present invention, it is possible to use a supervisory control signal which is wave-multiplexed and multiplexed with the main signal. Further, as the above-mentioned measurement signal, a wavelength tunable light source signal which is wavelength-multiplexed and multiplexed with the main signal can be used as in the method of the present invention.
The chromatic dispersion amount can be calculated from the wavelength dependence of the plurality of delay times obtained by repeating the measurement of the delay time while the node transmits the measurement signals of a plurality of wavelengths.

Further, the opposite node can return the measurement signal as it is as an optical signal or via optical / electrical conversion, as in the method of the present invention. Also, the above first
The node has crosstalk avoiding means, sends the measurement signal to the uplink or downlink of the first node, and the opposite node returns the measurement signal to the same line by the crosstalk avoiding means. be able to.

As a result, similarly to the method of the present invention, bidirectional measurement signals can be transmitted / received without crosstalk through one optical transmission line. Further, as the above-mentioned measurement signal, signals of different frequencies can be used on the same line as in the method of the present invention.

In the optical transmission system according to the present invention,
Similar to the method of the present invention, from the first node, simultaneously send out a plurality of measurement signals in the wavelength band not used as the main signal during line operation, and at the opposite node, extract the measurement signals and calculate their arrival time difference. It is also possible to measure the delay time and calculate the chromatic dispersion amount from the wavelength dependence of the delay time.

As a result, similarly to the method of the present invention, it is not necessary to return the measurement signal, and the method can be applied even when the uplink and the downlink are asymmetric between the nodes. In addition, in the optical transmission system according to the present invention, as in the method of the present invention, the first
From the node, a pulse signal of a frequency that does not substantially affect the main signal is superimposed on the main signal and sent out during line operation,
At the opposite node, measure the arrival time of the pulse signals,
The chromatic dispersion amount can also be calculated from the wavelength dependence of the delay time.

Further, in the above optical transmission system, when there are a plurality of opposite nodes, the first node selects the optimum optical transmission line based on the chromatic dispersion amount of each optical transmission line calculated as described above. You can select and switch. That is, the first node selects, for example, the optical transmission line having the minimum chromatic dispersion amount based on the chromatic dispersion amount of each optical transmission line calculated from the measurement signals returned from the plurality of opposite nodes, and You can switch.

In this case, the selection / switching of the optical transmission line can be performed for each wavelength. The measurement signal may be wavelength-division-multiplexed with the main signal according to the number of optical transmission lines. Further, the chromatic dispersion amount calculated as described above is exchanged between the respective nodes, and the first node can collect and accumulate the chromatic dispersion amount of each optical transmission line.

That is, the first node collects and accumulates the chromatic dispersion amount of each optical transmission line calculated by a plurality of opposite nodes, and thus, for example, the optical transmission line having the minimum chromatic dispersion amount, as described above. Can be selected and switched. Therefore, in the optical add / drop node and the optical cross-connect node, the path generally changes for each wavelength, so that when the path changes for each wavelength, it becomes possible to accumulate the chromatic dispersion amount for each wavelength.

A variable dispersion compensator for compensating the chromatic dispersion amount can be provided in the desired optical transmission line. That is, as described above, since the required amount of dispersion compensation is determined as a result of calculating the amount of chromatic dispersion, all wavelengths are collectively collected using the variable dispersion compensator (T-DC) arranged on the optical transmission line. Dispersion compensation can be realized at low cost by performing dispersion compensation.

The variable dispersion compensator may be provided for each wavelength or for each of a plurality of wavelength groups. Further, instead of the variable dispersion compensator, dispersion compensation fibers having different chromatic dispersion amounts and an optical switch for switching these dispersion compensation fibers according to the required chromatic dispersion amount may be used.

Further, when switching the optical transmission lines, the first node issues an alarm when the chromatic dispersion amount of the switching destination optical transmission line is larger than the chromatic dispersion amount of the working optical transmission line. You may do it. Furthermore, the first node above is
When the optical transmission line is switched, the dispersion compensation amount of the variable dispersion compensator can be reset according to the chromatic dispersion amount of the switching destination optical transmission line.

Furthermore, the wavelength dispersion amount may be compensated at the node where the wavelength conversion is performed. This makes it possible to minimize the waveform distortion due to the amount of chromatic dispersion at the subsequent nodes. Each node used in the above-described chromatic dispersion amount measuring method and optical transmission system according to the present invention extracts the received measurement signal and first means for transmitting the measurement signal together with the main signal during line operation. And a second means for returning the measurement signal, and the distance of the optical transmission line section is calculated from the delay time required for returning the measurement signal, and the chromatic dispersion amount of the optical transmission line section is calculated from the distance and the unique information of the optical transmission path. Third means to
It is characterized by having.

The above-mentioned measurement signal may be a supervisory control signal which is wavelength-multiplexed and multiplexed with the main signal. The measurement signal is a wavelength tunable light source signal that is wavelength-multiplexed and multiplexed with the main signal, the first means sends out the measurement signals having a plurality of wavelengths, and the third means delays the signals. The chromatic dispersion amount can be calculated from the wavelength dependence of the plurality of delay times obtained by repeating the time measurement.

Further, the above-mentioned second means can return the measurement signal as it is as an optical signal or via optical / electrical conversion. Further, the first means can send the measurement signal to the uplink or the downlink, and the second means can return the measurement signal to the same line by the crosstalk avoiding means.

Further, the node according to the present invention includes a first means for simultaneously transmitting a plurality of measurement signals in a wavelength band not used as a main signal during line operation, and a difference in arrival times between the received measurement signals. The second means for measuring the delay time and calculating the chromatic dispersion amount from the wavelength dependence of the delay time.

The node according to the present invention further comprises first means for superimposing a pulse signal having a frequency that does not substantially affect the main signal on the main signal and transmitting the superposed signal during line operation, and the received pulse signals. Second means for measuring the delay time from the arrival time difference and calculating the chromatic dispersion amount from the wavelength dependence of the delay time.

[0048]

1 shows an embodiment (1) of a method for measuring the amount of chromatic dispersion and an optical transmission system according to the present invention. In this embodiment, the nodes 1 and 2 constituting the optical transmission system are connected by an optical fiber transmission line 3 constituted by a forward path and a return path, and a main signal S _M is reciprocated.

Then, the node 1 (first node
The monitoring control channel signal S _CC , which is a measurement signal, is received from the node 2) which is the reception node.
It is configured to be sent back to the node 1 and then returned to the node 1.

The supervisory control channel signal S _CC is wavelength-division-multiplexed with the main signal S _M , as shown in FIG. At the node 1, the delay time T required for folding back the supervisory control channel signal S _CC
1 is measured, and the optical fiber transmission line 3 is measured from this delay time T1.
The distance L [Km] of is calculated.

Further, the node 1 selects the optical fiber transmission line 3 from the information of the type of the optical fiber transmission line registered by the maintenance person.
The peculiar dispersion coefficient [ps / nm / km] over all wavelengths of
The chromatic dispersion amount [PS / nm] in the node 1-2 section can be calculated. FIG. 2 shows an embodiment (2) of the chromatic dispersion amount measuring method and the optical transmission system according to the present invention. In this embodiment, unlike the above-mentioned embodiment (1), the wavelength tunable light source signal S _V generated from the wavelength tunable light source is used as the measurement signal.

At the node 1, the wavelength tunable light source signal S _V
The delay time T1 required for the turnaround is measured in the same manner as in the above Example (1) using the above method. In this case, the wavelength dependence of the delay time obtained by repeating the measurement while changing the wavelength (for each wavelength The chromatic dispersion amount can be calculated by the following formula from the delay time).

Β (λ) = − dT (λ) / dλ Equation (1) As a result, unlike the above embodiment (1), information on the amount of chromatic dispersion for each type of optical fiber becomes unnecessary, and in the future. It can flexibly support the expansion of various types of optical fibers. In addition, this wavelength tunable light source uses a wavelength control channel signal (OSC).
You may use as.

FIG. 3 shows an embodiment of the node 1 on the transmitting side in the above embodiments (1) and (2). First,
FIG. 1A shows an example of circuit configuration. In this circuit configuration example, a pulse generator (PG) 11 and a pulse signal from the pulse generator 11 are used as a transmission frame pulse FPS.
The phase difference measuring unit 12 and the framer 13 that are input as
Multiplexer 14 that multiplexes bits FLGRS, FLGR and DELAY, which will be described later, and main signal data to give to framer 13, main signal data from framer 13, and bit FL
A separation unit 15 for separating GR and DELAY, an electric / optical conversion unit 16 for converting an electric signal from the framer 13 into an optical signal and sending the optical signal to an opposite node, and an optical signal received from the opposite node for conversion to an electric signal. And an optical / electrical conversion unit 17 that operates.

The received frame pulse FPR extracted by the framer 13 is applied to the phase difference measuring section 12. First, the phase difference measuring unit 12 inserts a transmission flag FLGS and a reception flag FLGR, which are measurement signals, and a phase difference between transmission and reception frames, as shown in FIG. A bit DELAY (6 bits in the illustrated example) is prepared and given to the multiplexing unit 14.

As shown in FIG. 4B and 2, the transmission flag FLGS is set to "H" at the start of measurement. In the multiplexer 14, the above-mentioned bits FLGS / FLGR / DEL
The data DTS in which the main signal is multiplexed on AY is sent to the framer 13. In the framer 13, a signal for one frame to which the transmission frame pulse FPS from the pulse generator 11 is added is converted into an optical signal by the electric / optical conversion unit 16, and then the opposite node (Embodiments (1) and (2)). Then send to node 2).

The opposite node receiving this frame signal determines the phase difference (T2) of the transmission / reception frame by the phase difference bit D.
Insert it in the ELAY and, as shown in (2) of the figure,
A frame signal in which the reception frame pulse FPR is set to "H" is sent back (see (1) in the same figure).

In the node 1 which receives the returned frame signal, the optical / electrical converting section 17 and the framer 1 are connected.
The receiving unit FLGR and the phase difference bit DELAY are separated by the separating unit 15 via 3 and given to the phase difference measuring unit 12. In the phase difference measuring unit 12, the total delay time (T) of the transmission flag FLGS-reception flag FLGR that occurs between the round trips.
By subtracting the phase difference (T2) written in the phase difference bit DELAY from 1), the time required for the round trip can be measured.

This delay time (T1−T2) × group velocity in the optical fiber transmission line / 3/2 (see (2) in the same figure)
Thus, the distance L of the transmission line 3 is obtained. Further, the chromatic dispersion amount is obtained by giving a dispersion coefficient based on the information on the type of optical fiber (see (2) in the same figure).

Here, when the types of the optical fibers of the uplink and the downlink are different, it is possible to deal with them by giving different group velocities and dispersion coefficients respectively. In addition, by using data that also includes wavelength dependence as a dispersion coefficient, WDM
It is possible to perform a calculation that also incorporates the wavelength dependence.

FIG. 5 shows an embodiment of the node 2 on the receiving side shown in FIGS. The embodiment shown in FIG. 5 (1) employs a configuration in which the optical signal is returned as it is, and therefore the wavelength filters 21 and 22 are provided. Therefore, when the main signal S _M and the supervisory control channel signal S _CC that has been transmitted from node 1 is input to the node 2, the channel signal monitoring control by the wavelength filter 21 S _CC
Only the main signal S _{M is} separated and taken out and returned to the wavelength filter 22. Then, the supervisory control channel signal S _CC is returned from the wavelength filter 22 toward the node 1.

In this case, the optical amplification may be performed to recover the amplitude and then the optical signal may be folded back. Further, instead of folding all the power at the time of folding, the optical coupler may be used for branching so that a part of the power is returned. May be configured to perform optical / electrical conversion. In FIG. 2B, instead of returning the optical input signal as it is, the optical input signal is once converted into an electric signal and then converted back into an optical signal and sent back.

That is, in addition to the configuration shown in FIG. 1A, the node 2 has an optical / electrical converter 23 and an electrical / optical converter 24.
Are provided, and the supervisory control channel signal S _CC separated by the wavelength filter 21 is once converted into an electric signal by the electric / optical conversion unit 23 and dropped into the node 2 and then further electric / optical. The optical signal is converted back to the optical signal by the converter 24 and is sent back to the node 1 via the wavelength filter 22.

The embodiment of the node 2 shown in FIG. 5 shows only the structure for returning the signal, but in the case of the embodiment of FIG. 6, the embodiment (1) of the node 1 having both transmitting and receiving functions.
Is shown. That is, in this node 1, the wavelength filters 31 for the uplink and the downlink, respectively.
And 32 are provided, and the measurement signal S _CC separated by the wavelength filter 31 is applied to the optical / electrical conversion unit 34 via the optical circulator 33 as the crosstalk avoiding means.

When the optical / electrical converting section 34 receives the uplink measurement signal S _S , electric / electrical conversion is performed.
The measurement signal S _S similar to the downlink is sent from the optical conversion unit 35 to the opposite node from the wavelength filter 31 via the optical circulator 33.

Similarly, the wavelength filter 32 is provided with an optical circulator 36, an optical / electrical converter 37, and an electrical / optical converter 38, and the downlink measurement signal S _S sent from the opposite node on the right side. Is given from the optical wavelength filter 32 to the optical / electrical converter 37 via the optical circulator 36, and triggered by this, the upstream measurement signal S _S from the electrical / optical converter 38 is a node facing the wavelength filter 32. It will be sent to.

In this way, by avoiding the crosstalk between the signals of the up line and the down line, the bidirectional measurement signal is realized by one optical fiber. FIG. 7 shows an embodiment (2) obtained by modifying the embodiment (1) shown in FIG. In the case of this embodiment (2), the optical circulator 3
The difference is that wavelength filters 330 and 360 are used instead of 3 and 36.

That is, the measuring signal in this embodiment uses signals of two different wavelengths, that is, the signals S _S1 and S _S2 , which are the upstream signal and the downstream signal, respectively. Also in this embodiment, it is not necessary to use a separate optical fiber as the return line, and one signal is used by avoiding crosstalk between signals by using signals with different wavelengths for the uplink and downlink measurement signals. The two-way measurement signal is realized with the optical fiber of.

FIG. 8 shows an embodiment (3) of the method for measuring the amount of chromatic dispersion and the optical transmission system according to the present invention. In this embodiment, unlike the above embodiments (1) and (2), the measurement signal is sent from the node 1 and used in the node 2 without returning at the opposite node 2 to measure the chromatic dispersion amount. Is different.

That is, as shown in (2) of the figure, the wavelength band not used as the main signal S _M is, for example, 2 in this example.
The pulse S1 (wavelength λ1) and the pulse S2 (wavelength λ2) as one measurement signal are assigned, and these measurement pulses S
1 and S2 are simultaneously transmitted from the node 1.

Then, the opposite node 2 measures the delay time Δt when these measuring pulses S1 and S2 arrive.
Then, the chromatic dispersion amount for each wavelength can be calculated from the wavelength dependence of the delay time according to the equation (1) shown in the above embodiment (2).

As described above, since it is not necessary to return the measurement signal, as shown in (1) of the figure, there is an uplink and a downlink in which the node 4 is interposed between the node 1 and the node 2. It is also applicable to asymmetrical cases. In this case, the plurality of light sources may use, for example, two supervisory control channel signals separately prepared in a system of C band + L band. Further, by using a plurality of variable wavelength light sources having different operating wavelengths, it is possible to perform more accurate measurement regarding the above wavelength dependence.

FIG. 9 shows an embodiment (4) of the chromatic dispersion amount measuring method and the optical transmission system according to the present invention. In this embodiment, as shown in FIG. (1) and (2), the main signal S _M, superimposing a small pulse signal S _P sufficiently slow and modulation level than the signal rate (a / A) The maximum number of WDM wavelengths is used as the chromatic dispersion measurement signal, and measurement pulses are simultaneously transmitted from a plurality of wavelengths.
Then, the plurality of delay times can be obtained from the delay difference in arrival time between the pulses, and the dispersion amount for each wavelength can be obtained in the same manner as above from the wavelength dependence of the delay times.

As an example, the main signal is 10 Gb as shown in the figure.
Since it is a high-speed signal such as ps, it is 1 as a signal for measurement.
A low-speed signal such as Mbps may be used, and the degree of modulation may be a value that does not affect the transmission characteristics of the main signal. It is also possible to superimpose all the wavelength-multiplexed signals,
The measurement may be performed by superimposing only some wavelengths.

Further, instead of applying modulation in the same direction for all wavelengths, modulation is performed such that half of the wavelength is in the direction of decreasing the amplitude, and other wavelengths are in the direction of increasing the amplitude, thereby suppressing fluctuations in the overall power. It is also possible to suppress the level fluctuation of the optical output signal by using the method.

Since it is not necessary to return the measurement signal in the same manner as described above in this embodiment, it can be applied to the case where the uplink and the downlink are asymmetric. In each of the above embodiments, the method of measuring the chromatic dispersion amount between two nodes and the optical transmission system are shown as an example, but in FIG. 10, for measuring the chromatic dispersion amount in the case of having a plurality of opposite nodes. The example (1) of the optical transmission system of is shown.

That is, not only the node 1 and the node 2 are connected by the optical fiber transmission line 31, but the node 5 is further connected to the node 2 through the optical fiber transmission line 32. ing. In this case, the node 1 is a transmission node as an optical termination node (TERM), the node 5 is also a reception node as an optical termination node (TERM), and the node 2 is a relay amplification node (ILA). This constitutes an add / drop node (OADM) or an optical cross connect node (OXC).

Then, in each of the nodes 1, 2 and 5,
The chromatic dispersion amount measuring units 1a, 2a, and 5a for measuring the chromatic dispersion amount having the circuit configuration shown in FIG. 3 are provided respectively. These chromatic dispersion amount measuring unit 1
The a, 2a, and 5a can measure the chromatic dispersion amount as described above during the line operation. In this case, the chromatic dispersion amount may be always measured during the line operation.

That is, according to the embodiments (1) and (2) shown in FIGS. 1 and 2, the node 1 can measure the chromatic dispersion amount of the optical transmission line 31, and the node 2 can measure the chromatic dispersion amount.
The wavelength dispersion amount of 2 can be measured. Alternatively, according to the embodiments (3) and (4) of FIGS. 8 and 9, the nodes 2 and 5 can measure the chromatic dispersion amount of the optical transmission lines 31 and 32, respectively.

When the node 6 is newly added as shown in the figure, the node 1 can measure the chromatic dispersion amount of the optical transmission line 33 for the node 6 as well. In addition,
The chromatic dispersion amount measuring units 1a, 2a, 5a, 6a are provided with circuit configurations for transmission as shown in FIGS. 6 and 7, so that, for example, the node 2 can disperse the chromatic dispersion of both the optical transmission lines 31 and 32. It becomes possible to measure the amount during line operation.

The measurement of the chromatic dispersion amount is carried out at the time of adding a new node, starting a new span, increasing or decreasing wavelengths, switching optical add / drop nodes or optical cross-connect nodes, etc. May be carried out sequentially when is changed. Further, when a new span is added, measurement can be started for this path as well, so that the chromatic dispersion amount of the transmission path between all the nodes can be constantly monitored.

Therefore, in a WDM optical transmission system including optical add / drop nodes and optical cross-connect nodes that enable an infinite number of network structures, an accurate chromatic dispersion amount of a transmission line is required even when switching paths or expanding a transmission line. It becomes possible to grasp.

Targets for measuring the amount of chromatic dispersion as described above include optical transmission lines laid between nodes and optical components such as dispersion compensating fibers, filters, and optical amplifiers installed in the nodes. Among these, regarding the optical transmission line between the nodes, in addition to changing the optical transmission line used for switching the optical path, etc., the maintenance personnel can freely change the optical transmission line used. Therefore, the frequency of changes is considered to be high.

On the other hand, the in-apparatus optical parts such as the dispersion compensating fiber, the filter and the optical amplifier are not changed unless the parts are broken or recovered. Then, as shown in FIG. 11, for example, in the node 1, the chromatic dispersion amount measuring unit 1
a and 1b are provided, and the chromatic dispersion amount measuring unit 1a is the optical transmission line 3a.
The amount of dispersion beta ₀ is measured in the wavelength dispersion measuring unit 1b is separated to measure the chromatic dispersion beta ₁ of the optical fiber transmission line 3b, with respect to chromatic dispersion beta _i of the node 1 is registered in advance The number of measurements can be reduced by using the set value.

Alternatively, as shown in FIG. 12, between nodes
Not only the chromatic dispersion amount of the installed optical transmission line
Dispersion compensating fiber and filter installed in the cable, optical amplification
The chromatic dispersion of optical components such as containers should also be measured.
Therefore, the wavelength dispersion amount measuring units 1a and 1b are
Not only the transmission lines 3a and 3b, but also the dispersion amount β in the node _i
It is also possible to measure the total chromatic dispersion including
Yes.

As a result, even if a component in the node is changed due to a failure or the like, the line operation can be continued without resetting the information on the chromatic dispersion amount. In the optical transmission system example (1) shown in FIG. 10, the chromatic dispersion amount measuring unit is provided in each node, but the WDM optical transmission system includes a transmission node, a reception node, a relay amplification node, an optical add / drop node, Of the optical cross-connect nodes, only the optical add / drop node and the optical cross-connect node execute the optical path switching operation.

Therefore, as such an optical transmission system, as shown in FIG. 13, four optical termination nodes TERM are provided.
1 to TERM 4 as one optical cross connect node O
When path switching is performed via the XC, the chromatic dispersion amount is measured from this optical connect node OXC to the measurement sections (1) to (4) to save the number of nodes to be measured. Is also possible.

However, in this case, each optical terminal node TER
Regarding the relay amplification nodes ILA1 and ILA2 existing from M1 to the optical cross-connect node OXC, it is necessary to pass the measurement signal as it is. This also applies to the other relay amplification nodes ILA3 to ILA8.

FIG. 14 is a diagram in which the optical transmission system example (2) shown in FIG. 13 is further expanded and various nodes are installed. That is, the optical terminal node TE which is the transmitting node
RM1 and TERM2 are both optical cross-connect node O
It is connected to XC, and this optical cross connect node O
XC further includes relay amplification nodes ILA1 and IL
It is connected to A2. The relay amplification node ILA1 is further connected to the optical add / drop nodes OADM1 and OADM2. Similarly, the relay amplification node ILA2 is also connected to the optical add / drop nodes OADM1 and OADM2.

Optical add / drop node OADM
1 is an optical terminal node TERM3 as a receiving node
And the optical add / drop node OADM2 are connected to the optical terminal nodes TERM4 and TERM5.

The optical terminal node TERM3 is connected to the optical terminal node TERM6 which is a receiving node via the optical relay amplification nodes ILA3 to ILA5. In addition,
The β _i value shown between the nodes indicates the amount of chromatic dispersion between the nodes.

Therefore, by exchanging the chromatic dispersion amount β _i between the nodes as described above, the measured values of the dispersion amount between the nodes can be accumulated, and the accumulated values can be accumulated in the respective optical paths. It is possible to monitor the total chromatic dispersion amount. In addition, in the optical add / drop node and the optical cross-connect node, since the path generally changes depending on the wavelength, it is necessary to collect the cumulative value for each wavelength.

As described above, since the total value of the chromatic dispersion amount is known for each path, the route with the smallest chromatic dispersion amount can be selected as the optimum path. That is, FIG.
In the example of No. 4, path A (TERM1 → OX
C → ILA2 → OADM2 → TERM4) cumulative value of wavelength dispersion amount (β _A = β ₁ + β ₆ + β ₇ + β ₈ ) and path B indicated by a dotted line (TERM1 → OXC → ILA1 → OADM1 →
Cumulative value of chromatic dispersion of TERM4) (β _B = β ₁ + β ₂ +
By comparing the β ₃ + β ₅₎ and, for example, when having a small chromatic dispersion towards the path _{A (β A <β B)} , optical cross-connect node OXC and optical add-drop node OADM2 path A Will be selected.

FIG. 15 shows an example (1) of the procedure for collecting the amount of chromatic dispersion in the path B shown in FIG. In this embodiment, the optical cross connect node OXC is set in advance as a node for collecting the chromatic dispersion amount for this path B. Therefore, the optical cross connect node O
First, the XC sends the measured value of the chromatic dispersion amount to the transmitting node TE.
Requests are made to the RM1, the relay amplification node ILA2, and the optical add / drop node OADM2.

Then, in response to this, the transmitting node TE
The RM1, the relay amplification node ILA2, and the optical add / drop node OADM2 are respectively chromatic dispersion amounts β ₁ and β ₇ measured by themselves.
And β ₈ are returned. Then, the optical cross-connect node OXC, at the time when the chromatic dispersion amounts are equalized, its cumulative value Σβ
Calculate _i .

If necessary, the total chromatic dispersion amount is transmitted to the node TERM4. Such a sequence is repeated at a constant cycle. Figure 15
In the case of the procedure example (1) shown in (1), since there is one optical cross-connect node, the optical cross-connect node OXC may monitor all paths, but when there are a plurality of optical cross-connect nodes, the master Since there are multiple nodes, it is necessary to determine the range to be monitored in advance.

Since the chromatic dispersion amount collection procedure example (2) shown in FIG. 16 corresponds to such a case, the optical cross-connect node OXC1 includes an optical terminal node TERM1, relay nodes ILA1 and ILA2, and an optical terminal node. TERM3
The optical cross-connect node OXC2 is set so as to monitor the path 100 configured by and the other optical cross-connect node OXC2 monitors the path 200 configured by the relay amplification node ILA3 and the optical termination node TERM4. The functions of each other can be shared.

Then, the information of the amount of chromatic dispersion held by each other is exchanged, and the setting value is transmitted to another node if necessary. If the chromatic dispersion amount for determining the optimum path is determined as described above, this chromatic dispersion amount can be compensated. That is, if the dispersion compensation of the optical path A (see FIG. 14) is performed using the variable dispersion compensator (T-DC) arranged on the optical transmission line, the dispersion compensation can be realized at low cost. Become.

FIG. 17 shows an example of compensation of such a wavelength dispersion amount.
(1) is shown. In this example, the variable dispersion compensator T-
Show a configuration example in which DC is installed in the receiving node TERM4
There is. In this case, it is accumulated in each channel by the previous stage.
Chromatic dispersion amount Σβ_i= Β₁+ Β ₆+ Β₇+ Β₈The best
The control is performed so that compensation can be made.

That is, Σβ _i + variable dispersion compensator T-D
The wavelength dispersion amount of C is adjusted so that β _T = “0”. This variable dispersion compensator T-DC is disclosed in US Pat.
As described in 5,930,045 and 969,866,
This is a well-known technique.

A plurality of such variable dispersion compensators T-DC may be installed on the network and their mutual setting values may be adjusted to obtain the best dispersion compensation amount. If the variable dispersion compensator T-DC can adjust the wavelength characteristic, the set value may be changed for each wavelength according to the amount of dispersion for each wavelength.

Such an example is shown as a compensation example (2) in FIG. That is, in the case of the compensation example (1), the WDM optical signals are collectively subjected to dispersion compensation, but in order to compensate for the dispersion amount which differs for each wavelength, the dispersion is compensated for at the receiving node TERM4. A demultiplexer 41 for demultiplexing an optical signal and a variable dispersion compensator 42 for wavelengths λ _{A to} λ _C demultiplexed from the demultiplexer 41, respectively.
.About.44 can be used to set the dispersion compensation amount.

Further, the method of dividing into a plurality of wavelengths may be divided into channels having similar wavelengths, or may be divided into channels which follow the same path. Further, as an example (3) of compensating the chromatic dispersion amount, as shown in FIG. 19, instead of the variable dispersion compensator T-DC, a dispersion compensating fiber is provided in the receiving node TERM3 as shown in FIG. It is also possible to switch the dispersion compensation amount by switching the optical switches 51 to 55 according to the required dispersion compensation amount.

In this example, the dispersion compensating fibers 52 to 54 are arranged in parallel, but the dispersion compensating fibers 52 to 54 are connected in series and the connection destination is switched by the optical switch. Is also good. In this case, finer chromatic dispersion amount control can be performed. Further, the variable dispersion compensator T-DC as described above may be further combined therewith.

FIG. 20 shows a compensation example (4) of the chromatic dispersion amount. In this case, the total value of the chromatic dispersion amount of the switching destination path B with respect to the working path A is calculated in advance. If the calculated chromatic dispersion amount is larger than the chromatic dispersion amount of the path A, or if it is larger than a preset threshold value for suppressing the characteristic deterioration, the transmission characteristic of the main signal may be deteriorated. The optical cross-connect node OXC, which determines that there is a path switch, issues an alarm.

It is possible to issue such an alarm for all wavelengths having the same path.
The alarm may be issued in wavelength units including the wavelength dependence of the amount of dispersion. Note that when the alarm is not issued, that is, when the cumulative chromatic dispersion amount after switching is smaller than the working cumulative chromatic dispersion amount, the optical cross-connect node OXC does not switch from the path A to the path B. Needless to say.

Further, a switch whose transfer amount is smaller than a preset threshold for suppressing the characteristic deterioration may be selected as the switching destination. Furthermore, when it is better to leave a certain amount of dispersion, it is possible to select the switching destination path having the wavelength dispersion amount closest to the working path from the switching destinations.

In the case of performing such path switching, as shown in the compensation example (5) shown in FIG. 21, the cumulative dispersion amount of the switching destination is calculated at the time of path switching, and the dispersion amount on the path is reduced so that the dispersion amount becomes small. It may be configured to prevent the deterioration of the transmission characteristics after switching by resetting the dispersion compensation amount of the variable dispersion compensator T-DC provided in the above.

Further, by installing a plurality of variable dispersion compensators T-DC on the network, the dispersion amount is adjusted at a location or distribution where the dispersion amount of the active line not related to switching does not change. It may be possible to prevent the deterioration of the characteristics. FIG. 22 shows an embodiment of a node using wavelength conversion. In this example, a demultiplexer 61 of 1 × M, an optical switch 63 of N × N, and a demultiplexer of N × 1 are used to perform demultiplexing. Wavelength converter 6 between the device 61 and the optical switch 63.
2 illustrates a configuration example of an optical cross connect node that performs wavelength conversion by inserting 2.

In this structure, the path is switched by changing the wavelength of the signal. Normally, the receiving node is set to minimize the accumulated chromatic dispersion amount, but in an optical cross connect node using such wavelength conversion, if the waveform at the wavelength conversion point is distorted due to dispersion, No effective characteristic can be obtained for the waveform either, and this cannot be compensated for in the transmission line thereafter.

Therefore, as shown in the compensation example (6) of the chromatic dispersion amount in FIG. 23, the wavelength conversion optical cross-connect node OXC is configured to minimize not only the reception node but also the accumulated chromatic dispersion amount at the wavelength conversion point. By installing a variable dispersion compensator T-DC to compensate for the amount of chromatic dispersion, it is possible to support a wavelength conversion optical cross connect node.

In this case, the wavelength converter may be a transponder that performs optical / electrical conversion once, and again performs electrical / optical conversion using a laser having a different wavelength, or transmits. It is also possible to perform wavelength conversion with the optical signal as it is without converting the optical signal into an electrical signal, such as a wavelength converter using a non-linear effect.

(Supplementary Note 1) The first step of transmitting the measurement signal together with the main signal from the first node during line operation, the second step of extracting and returning the measurement signal at the opposite node, and the first step. A third step of calculating the distance of the optical transmission line between the nodes by measuring the delay time required for the return of the measurement signal at the node, and calculating the chromatic dispersion amount of the optical transmission line based on the distance; A method for measuring the amount of chromatic dispersion, comprising:

(Supplementary Note 2) In Supplementary Note 1, the measurement signal is a supervisory control signal that is wavelength-multiplexed and multiplexed with the main signal, and a method of measuring a chromatic dispersion amount. (Supplementary Note 3) In Supplementary Note 1, the measurement signal is a wavelength tunable light source signal that is wavelength-multiplexed and multiplexed with the main signal, and the measurement signals of a plurality of wavelengths are transmitted in the first step. A dispersion amount measuring method, wherein the chromatic dispersion amount is calculated from wavelength dependences of a plurality of the delay times obtained by repeating the measurement of the delay time in three steps.

(Supplementary Note 4) In any one of Supplementary Notes 1 to 3, the second step is characterized in that the measurement signal is folded back as an optical signal as it is or through an optical / electrical conversion. How to measure the amount of dispersion. (Additional remark 5) In any one of additional remarks 1 to 4, the first
A chromatic dispersion amount characterized in that the step sends the measurement signal to the uplink or the downlink of the first node, and the second step returns the measurement signal to the same line by avoiding crosstalk. Measuring method.

(Supplementary Note 6) In Supplementary Note 5, a chromatic dispersion amount measuring method is characterized in that, as the measurement signal, signals of different frequencies are used on the same line. (Supplementary note 7) The first step of simultaneously transmitting a plurality of measurement signals in the wavelength band not used as the main signal from the first node during line operation, and extracting the measurement signals at the opposite node and determining the arrival time difference A second step of measuring the delay time and calculating the chromatic dispersion amount from the wavelength dependence of the delay time;
A method for measuring the amount of chromatic dispersion, comprising:

(Supplementary Note 8) The first step of superimposing a pulse signal having a frequency that does not substantially affect the main signal on the main signal and sending the pulse signal during line operation, and A second step of measuring a delay time from the arrival time difference between pulse signals and calculating the chromatic dispersion quantity from the wavelength dependence of the delay time, the chromatic dispersion quantity measuring method.

(Supplementary Note 9) In an optical transmission system composed of a plurality of nodes, a measurement signal together with a main signal is transmitted from the first node during line operation, and the opposite node extracts the measurement signal and returns it. , Measuring the delay time required for returning the measurement signal at the first node to calculate the distance of the optical transmission line between the nodes, and calculating the chromatic dispersion amount of the optical transmission line based on the distance. Optical transmission system characterized by.

(Supplementary note 10) The optical transmission system according to claim 9, wherein the measurement signal is a supervisory control signal that is wavelength-multiplexed and multiplexed with the main signal. (Supplementary Note 11) In Supplementary Note 9, the measurement signal is a variable wavelength light source signal that is wavelength-multiplexed and multiplexed with the main signal,
The first node transmits the measurement signals of a plurality of wavelengths, and calculates the chromatic dispersion amount from the wavelength dependence of the plurality of delay times obtained by repeating the measurement of the delay times. Optical transmission system.

(Supplementary Note 12) In any one of Supplementary Notes 9 to 11, the optical signal is characterized in that the opposite node folds back the measurement signal as an optical signal or via an optical / electrical conversion. Transmission system. (Supplementary note 13) In any one of supplementary notes 9 to 12,
The first node has crosstalk avoiding means, and sends the measurement signal to the uplink or downlink of the first node,
An optical transmission system, wherein the opposite node returns the measurement signal to the same line by the crosstalk avoiding means.

(Supplementary Note 14) The optical transmission system according to Supplementary Note 7, wherein signals of different frequencies are used on the same line as the measurement signal. (Appendix 15) In an optical transmission system including a plurality of nodes, a plurality of measurement signals in a wavelength band not used as a main signal are simultaneously transmitted from the first node during line operation, and the opposite node uses the measurement signals. An optical transmission system characterized in that a signal is extracted, a delay time is measured from the arrival time difference, and a chromatic dispersion amount is calculated from the wavelength dependence of the delay time.

(Supplementary Note 16) In an optical transmission system composed of a plurality of nodes, a pulse signal of a frequency that does not substantially affect the main signal is superimposed on the main signal from the first node during the line operation. An optical transmission system which is characterized by transmitting, measuring the arrival time of the pulse signals at opposite nodes, and calculating the chromatic dispersion amount from the wavelength dependence of the delay time.

(Supplementary Note 17) In any one of Supplementary Notes 9 to 14, there are a plurality of the opposite nodes, and the first node has an optimum optical wavelength based on the calculated chromatic dispersion amount of each optical transmission line. An optical transmission system characterized by selecting and switching transmission lines.

(Supplementary note 18) In any one of supplementary notes 9 to 14, the optical transmission is characterized in that the measurement signal is wavelength-division-multiplexed with the main signal in accordance with the number of the optical transmission paths. system. (Supplementary note 19) The optical transmission system according to supplementary note 17, wherein the calculated chromatic dispersion amount is exchanged between the respective nodes, and the first node collects and accumulates the chromatic dispersion amount of each optical transmission line. .

(Supplementary Note 20) The optical transmission system according to Supplementary Note 19, wherein a variable dispersion compensator for compensating the chromatic dispersion amount is provided in a desired optical transmission line. (Supplementary Note 21) In Supplementary Note 20, the variable dispersion compensator is
An optical transmission system characterized by being provided for each wavelength or for each of a plurality of wavelength groups.

(Supplementary Note 22) In Supplementary Note 20, instead of the variable dispersion compensator, a dispersion compensating fiber having a different chromatic dispersion amount and an optical switch for switching these fibers according to a required chromatic dispersion amount are used. Optical transmission system characterized by.

(Supplementary Note 23) In any one of Supplementary Notes 17 to 22, when the first node switches the optical transmission line, the wavelength of the optical transmission line of the switching destination is more than the chromatic dispersion amount of the working optical transmission line. An optical transmission system characterized by issuing an alarm when the amount of dispersion becomes larger.

(Supplementary Note 24) In Supplementary Note 20, when switching the optical transmission line, the first node sets the dispersion compensation amount of the variable dispersion compensator in accordance with the chromatic dispersion amount of the optical transmission line of the switching destination. An optical transmission system characterized by resetting.

(Supplementary Note 25) In Supplementary Note 20 or 21,
An optical transmission system characterized in that a node performing wavelength conversion compensates for the amount of chromatic dispersion. (Supplementary note 26) First means for transmitting a measurement signal together with a main signal during line operation, second means for extracting and folding back the received measurement signal, and an optical signal from the delay time required for folding back the measurement signal. A third means for calculating the distance of the transmission path section and calculating the chromatic dispersion amount of the optical transmission path section based on the distance.

(Supplementary note 27) The node according to Supplementary note 26, wherein the measurement signal is a supervisory control signal that is wave-weight division multiplexed with the main signal. (Supplementary note 28) In Supplementary note 26, the measurement signal is a wavelength tunable light source signal that is wavelength-multiplexed and multiplexed with the main signal, and the first means sends out the measurement signals of a plurality of wavelengths, A node characterized in that the chromatic dispersion amount is calculated from a plurality of wavelength dependences of the delay times obtained by repeating the measurement of the delay times by three means.

(Supplementary Note 29) In any one of Supplementary Notes 26 to 28, it is characterized in that the second means folds back the measurement signal as an optical signal or through an optical / electrical conversion. node. (Supplementary note 30) In any one of Supplementary notes 26 to 29, the first means sends the measurement signal to an uplink or a downlink, and the second means crosses the measurement signal to the same line. A node characterized by being folded back by a talk avoidance means.

(Supplementary Note 31) In the supplementary note 30, a node characterized by using signals of different frequencies on the same line as the measurement signal. (Supplementary Note 32) First means for simultaneously transmitting a plurality of measurement signals in a wavelength band not used as a main signal during line operation,
A second means for extracting the received measurement signal, measuring the delay time from the arrival time difference, and calculating the chromatic dispersion amount from the wavelength dependence of the delay time.

(Supplementary Note 33) From the first means for superimposing a pulse signal having a frequency that does not substantially affect the main signal on the main signal and transmitting it during line operation, and the difference in arrival time between the received pulse signals. A second means for measuring the delay time and calculating the chromatic dispersion amount from the wavelength dependence of the delay time.

[0134]

As described above, according to the chromatic dispersion amount measuring method and the optical transmission system, the measurement signal together with the main signal is transmitted from the first node during the line operation, and the opposite node transmits the measurement signal. Is extracted and returned, the delay time required for returning the measurement signal is measured at the first node, the distance of the optical transmission line between the nodes is calculated, and the wavelength dispersion of the optical transmission line is calculated based on the distance. Since it is configured to calculate the amount, it is possible to measure the chromatic dispersion amount of the transmission line in real time during operation of the signal line.

Further, the first node superimposes on the main signal a plurality of signals in the wavelength band not used as the main signal or a pulse signal having a frequency that does not substantially affect the main signal, and sends out the signal during line operation. It is also possible to extract the measurement signal at the opposite node, measure the delay time from the arrival time difference, and calculate the chromatic dispersion amount from the wavelength dependence of the delay time to determine the wavelength of the optical transmission line between the nodes during line operation. It is possible to measure the amount of dispersion.

Furthermore, there are a plurality of opposite nodes, and the first node
Since the node is configured to select and switch the optimum optical transmission line based on the calculated or collected chromatic dispersion amount of each optical transmission line, it is possible to always realize high-quality optical transmission.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment (1) of a chromatic dispersion amount measuring method and an optical transmission system according to the present invention.

FIG. 2 is a diagram showing an embodiment (2) of the chromatic dispersion amount measuring method and the optical transmission system according to the present invention.

FIG. 3 is a diagram showing an embodiment of a node (transmission side) used in the present invention.

FIG. 4 is a conceptual diagram of calculating a chromatic dispersion amount according to the present invention.

FIG. 5 is a block diagram showing an embodiment of a node (reception side) used in the present invention.

FIG. 6 is a diagram showing an embodiment (1) of a node (transmission / reception side) used in the present invention.

FIG. 7 is a diagram showing an embodiment (2) of a node (transmission / reception side) used in the present invention.

FIG. 8 is a diagram showing an embodiment (3) of the chromatic dispersion amount measuring method and the optical transmission system according to the present invention.

FIG. 9 is a diagram showing an embodiment (4) of the chromatic dispersion amount measuring method and the optical transmission system according to the present invention.

FIG. 10 is a block diagram showing an example (1) of an optical transmission system for measuring the amount of chromatic dispersion according to the present invention.

FIG. 11 is a diagram showing an example in which the in-node chromatic dispersion amount is not considered in the measurement of the chromatic dispersion amount according to the present invention.

FIG. 12 is a diagram showing an example in which the in-node chromatic dispersion amount is taken into consideration in the measurement of the chromatic dispersion amount according to the present invention.

FIG. 13 is a block diagram showing an example (2) of an optical transmission system for measuring the amount of chromatic dispersion according to the present invention.

FIG. 14 is a block diagram showing an example of selecting an optimum path in the optical transmission system example (3) for measuring the amount of chromatic dispersion according to the present invention.

FIG. 15 is an example of a procedure for collecting chromatic dispersion according to the present invention (1)
It is the block diagram which showed.

FIG. 16 is an example of a chromatic dispersion amount collection procedure example (2) according to the present invention.
It is the block diagram which showed.

FIG. 17 is a block diagram showing a compensation example (1) of a chromatic dispersion amount according to the present invention.

FIG. 18 is a block diagram showing a compensation example (2) of the chromatic dispersion amount according to the present invention.

FIG. 19 is a block diagram showing a compensation example (3) of the chromatic dispersion amount according to the present invention.

FIG. 20 is a block diagram showing an example (4) of compensating the amount of chromatic dispersion according to the present invention.

FIG. 21 is a block diagram showing an example (5) of compensating the amount of chromatic dispersion according to the present invention.

FIG. 22 is a block diagram showing an embodiment of a node using wavelength conversion according to the present invention.

FIG. 23 is a block diagram showing an example (6) of compensating a chromatic dispersion amount according to the present invention.

FIG. 24 is a block diagram showing an example of a conventionally known optical transmission system.

FIG. 25 is a diagram for explaining the accumulation of chromatic dispersion amounts.

[Explanation of symbols]

1, 2, 4-6 Nodes 3, 31-33, 3a, 3b Optical fiber transmission lines 21, 22, 31, 32, 330, 360 Wavelength filters 23, 34, 37 Optical / electrical converter (O / E) 24 , 35, 38 Electric / optical conversion unit (E / O) 33, 36 Optical circulator 1a, 2a, 5a, 6a Chromatic dispersion measurement unit OXC Optical cross-connect node TERM Optical termination node (transmission node, reception node) ILA Intermediate amplification Node OADM In the optical add / drop node diagram, the same reference numerals indicate the same or corresponding parts.

Continued front page    F term (reference) 5K002 AA05 AA06 CA01 DA02 EA06                       EA32 FA01 GA03

Claims (10)

[Claims] 1. A first step of transmitting a measurement signal together with a main signal from a first node during line operation, a second step of extracting and returning the measurement signal at an opposite node, and a first node at the first node. A third step of measuring a delay time required for returning the measurement signal, calculating a distance of the optical transmission line between the nodes, and calculating a chromatic dispersion amount of the optical transmission line based on the distance. A method for measuring the amount of chromatic dispersion, which is characterized in that 2. A first step of simultaneously transmitting a plurality of measurement signals in a wavelength band not used as a main signal from the first node during line operation, and a difference in arrival time between the measurement signals extracted by the opposite node. And a second step of calculating a chromatic dispersion amount from the wavelength dependence of the delay time, and a chromatic dispersion amount measuring method. 3. A first step of superimposing a pulse signal having a frequency that does not substantially affect the main signal on the main signal and transmitting the pulse signal during line operation from the first node; A chromatic dispersion amount measuring method comprising: a second step of measuring a delay time from the arrival time difference between the two and calculating a chromatic dispersion amount from the wavelength dependence of the delay time. 4. An optical transmission system composed of a plurality of nodes, wherein a measurement signal together with a main signal is transmitted from a first node during line operation, and an opposite node extracts and returns the measurement signal. The first node measures a delay time required for returning the measurement signal, calculates a distance of the optical transmission line between the nodes, and calculates a chromatic dispersion amount of the optical transmission line based on the distance. Optical transmission system. 5. In an optical transmission system composed of a plurality of nodes, a plurality of measurement signals in a wavelength band not used as a main signal are simultaneously transmitted from a first node during line operation, and the measurement is performed at an opposite node. An optical transmission system characterized in that a signal for use is extracted, a delay time is measured from the arrival time difference, and a chromatic dispersion amount is calculated from the wavelength dependence of the delay time. 6. An optical transmission system composed of a plurality of nodes, wherein a pulse signal of a frequency that does not substantially affect the main signal is superimposed on the main signal and is sent out during line operation from the first node. , Measure the arrival time of the pulse signals at the opposite node,
An optical transmission system characterized in that a chromatic dispersion amount is calculated from the wavelength dependence of the delay time. 7. The apparatus according to claim 6, wherein there are a plurality of the opposite nodes, and the first node selects and switches an optimum optical transmission line based on the calculated chromatic dispersion amount of each optical transmission line. An optical transmission system characterized by that. 8. A first means for transmitting a measurement signal together with a main signal during line operation, a second means for extracting the received measurement signal and returning it, and a delay time required for returning the measurement signal. A third means for calculating the distance of the optical transmission path section and calculating the chromatic dispersion amount of the optical transmission path section based on the distance. 9. A first means for simultaneously transmitting a plurality of measurement signals in a wavelength band not used as a main signal during line operation, and a received measurement signal is extracted and a delay time is measured from the arrival time difference between the first measurement signal and the second measurement signal. A second means for calculating a chromatic dispersion amount from the wavelength dependence of the delay time, and a node. 10. A first means for superimposing a pulse signal having a frequency that does not substantially affect the main signal on the main signal and transmitting the superposed signal during line operation, and a delay time based on an arrival time difference between the received pulse signals. And a second means for calculating the chromatic dispersion amount from the wavelength dependence of the delay time, and a node.